*R.J. Harrington 1 , S.C. Gray 1 , C.E. Ramos-Scharrón 2 , B. O’Shea 1

1. *R.J. Harrington1, S.C. Gray1, C.E. Ramos-Scharrón2, B. O’Shea1 1University of San Diego, Department of Marine and Environmental Studies, San Diego, CA 92110 2 University of Texas at Austin, Department of Geography and the Environment, Austin, TX 78712 *RobertHarrington@sandiego.edu Introduction: HCA Dendrogram Land development on high relief islands, particularly in the form of unpaved roads, has the potential to increase surface erosion and enhance the contribution of land-based sediments and associated metals (i.e., Fe, Al, Ti, Ba, Cu, Zr, Zn, K) to the marine environment. High concentrations of metals in sediment are of concern because they may bioaccumulate in some benthic invertebrates (Williams et al. 2010). The island of St. John in the US Virgin Islands (Fig. 1 at right) is a steep volcanic island surrounded by fringing coral reefs. St. John is an ideal location to study how watershed development may be impacting metal accumulation in sensitive coral reef habitats because: a) elevated concentrations of metals have been found in St. John’s hydrothermally-altered bedrock and soils (relative to surrounding unaltered bedrock); b) land protected under the Virgin Islands National Park makes the comparison of undeveloped and developed areas viable; and c) previous research on St. John has demonstrated that human activities (especially the building of unpaved roads) have increased watershed sediment yields (Ramos-Scharrón and MacDonald 2007), terrigenous sediment accumulation in the marine environment (Gray et al., 2012), and sedimentation rates by 3-4 times the long-term historic rates (Brooks et al. 2007). Objectives: In order to better understand the linkages between terrigenous erosion and marine deposition of metals on St. John, our study objectives were to: 1) identify which major and trace elements originate from the watershed and are deposited in the marine environment around St. John; 2) describe how the mineralogy and concentration of major and trace elements vary spatially from ridge to reef; 3) quantify any differences between developed and undeveloped watershed-bay pairings in terms of a) major and trace elemental concentrations and b) metal flux; and 4) describe whether developed vs. undeveloped differences in major and trace element concentrations and flux in the marine environment were consistent with watershed-scale modeled sediment yield rates. Figure 2. (Left) Field sampling of a bedrock outcrop in Coral Bay Watershed. (Center) Stream sediments were collected with silt-fence sediment trap. (Right) Marine samples were collected using a sediment trap consisting of PVC tubes set 60 cm above the ocean floor. Results: Petrography & mineralogy.Petrographic and XRD analyses of plagiorhyolite and basalt (Fig. 3) demonstrate that the bedrock units (Water Island Fm.), stream bed sediments, and the terrigenous component of the marine sediments were generally similar in composition and composed of mostly albite, quartz, chlorite (plagiorhyolite), plagioclase, clinopyroxene, epidote, chlorite, and opaque minerals (basalt). Watershed-derived major and trace elements. In order to determine which of the 29 metals measured were most likely to have been conservatively transported from the watershed to the marine environment, the major and trace element concentrations were compared to the proportion of terrigenous sediment in 12 marine samples collected in marine sediment traps. Five major and trace elements (FeO, Al2O3, TiO2, Cu, Zr) were strongly correlated (R2 = 0.80 - 0.94) and three (Ba, Zn, K2O) were moderately correlated (R2= 0.72 - 0.79) with percent terrigenous sediment (Fig.4). This suggests that the major and trace elements TiO2, FeO, Al2O3, Cu, and Zr may be indicators for terrigenous source material. Ridge to reef assessment of metal concentrations and mineralogy in rocks and sediments on St. John, U.S. Virgin Islands. A total of 63 geologic (hydrothermally altered [n=4] and non-hydrothermally altered bedrock [n=14], soil [n=20], and stream bed [n=11]) samples, were collected by hand or in silt-fence sediment traps from within the developed (Coral Bay) and undeveloped (Little Lameshur) watersheds (Fig. 2). Shore and reef sediments (n=14) were collected in marine sediment traps over a 26 day period (Fig. 2). The mineralogy of all samples was determined by petrography & XRD, and 10 major and 19 trace element concentrations were measured by XRF. Principle component analysis (PCA) correlated samples that were then plotted into 2 dimensional space. Hierarchical cluster analysis (HCA) grouped samples with similar major and trace element concentrations. The percent terrigenous sediment for each marine sample was analyzed by LOI (Loss on Ignition), and metal flux rates to the marine environment were calculated. Sediment production rates from unpaved roads were measured with silt-fence sediment traps in 1998-2000 (n =76 measurements) and in 2010-2011 (n = 25 measurements). Multiple-linear regression analyses were used to develop a road-segment scale erosion model that was incorporated into a GIS system to estimate the contribution of roads into watershed- and sub-watershed-scale sediment yields. Figure 1. St. John, U.S. Virgin Islands (Top Left). Eastern St. John, the study area (Bottom) showing sample locations within and below developed (Coral Bay) (shaded in light green) and undeveloped (Little Lameshur) (shaded light brown) watersheds. Sample types are depicted as different shaped symbols. The sample shapes are colored according to their grouping by hierarchical cluster analysis (HCA) as shown in the dendrogram (middle right). Orange shading shows the general location of hydrothermally altered bedrock. Figure 3.Rock and sediment thin section photomicrographs shown in order from ridge (top) to reef (bottom). Stream bed sediments contain rhyolite (A) and basalt grains (B) and Reef trap sediments contain rhyolite (A) and carbonate grains (B). Methods: Geochemical Grouping. HCA of major and trace elements generally grouped samples of similar geographic locations and similar sample types (Fig. 1). Marine shore sediments collected below the developed watershed were more similar geochemically to the bedrock sediments than were those collected below the undeveloped watershed. Principle components, PC1 and PC2, accounted for 67% and 61% of the variance in the major and trace element concentrations, respectively (Fig. 6). The PCA of watershed rocks and sediments collected in developed and undeveloped watersheds overlapped, suggesting generally similar geochemical composition of watershed rocks. PCA generally grouped marine and watershed samples separately but the geochemistry of some of the marine shore samples in the developed area grouped with the watershed samples (Fig. 6). Developed/Undeveloped differences in element concentrations and flux rates. Major and trace element concentrations and flux rates (in 10 marine sediment traps) were greater at the shore than on reef environments and always greater below the developed watersheds (Table 1, Figure 7). Modeled sediment delivery and yields. Estimated sediment yields into Coral Bay from its highly developed watershed were 517 Mg yr-1, or 12.6 times higher than the 41 Mg yr-1 yields reaching Lameshur Bay. Figure 4.Correlations between percent terrigenous material and major element (above) and trace element (below) concentrations in marine sediments. Zn, Ba, and K2O were also correlated with R2 of 0.80, 0.79, and 0.72, and P-values of < 0.001 respectively. Table2. Watershed size, sediment delivery and yield estimates from (Ramos-Scharrón and MacDonald 2007, Ramos-Scharrón et al. 2012). Ratios between developed areas and undeveloped areas are calculated for comparison. Figure 7. Ratios of developed to undeveloped major and trace element concentrations and flux rates for the shore (solid color) and reef (diagonal lines) (Table 1) are displayed. Undeveloped (Lameshur Bay) Ridge to reef variation.The ranges of major and trace element concentrations measured in samples collected in the watersheds (bedrock, soil, stream) generally do not appear to differ from each other. Median major and trace element concentrations were always higher in the rock and sediment samples collected in the watershed sites compared to those collected at the reef sites and the shore sites below undeveloped watersheds (Fig. 5). However, median major and trace element concentrations in sediment collected at the shore sites below developed watersheds were similar to concentrations at watershed sites. Major and trace element concentrations of all sediment types were usually higher (and more variable) in the developed compared to the undeveloped locations (Fig. 5). Developed (Coral Bay) Conclusion: Figure 5. Box and whisker plots showing variation in median metal concentrations from ridge to reef in the undeveloped (left) compared to the developed (right) watershed. The box represents the inter quartile range (IQR) between the 25th and 75th percentile, and the whiskers represent a value 1.5 times the IQR above and below the 75thand the 25th percentile. The median is the center line in the box. The dots show outliers. The ridge to reef concentration patterns of Zn, Ba, and K were similar to those depicted above. Figure 6. PCA results for different sample types using major element percentages (left graphs) and trace element concentrations (right graphs). The upper graphs compare PCA results between sample types and the lower graphs compare PCA results between samples collected in developed and undeveloped areas. For the major elements, a positive PC1 = higher CaO and lower SiO2 and Al2O3 and a positive PC2 = higher FeO and MnO and lower K2O concentrations. For the trace elements, a positive PC1 = higher Ni, Cr, and V and lower Rb and Zr and a positive PC2 = higher Ba and Zr and lower Sr. Two separate groups are displayed: a terrigenous group (shaded light gray) and a marine group (shaded light blue). The major and trace-element concentrations as well as the mineralogy of marine terrigenous sediments demonstrate a watershed source for some major and trace elements. Near-shore sediments in the developed areas were characterized by mineralogy and major and trace element concentrations similar to watershed rocks and sediments, suggesting a strong watershed influence in the developed areas. However, near shore sediments below the undeveloped watershed contained less watershed derived metals and minerals. Marine major and trace element concentrations were typically between 5 and 10 times higher at developed compared to the undeveloped shore sites and between 2 to 52 times higher at developed compared to undeveloped reef sites. Marine metal flux rates were typically between 2 to 7 times higher at developed shore sites and 33 to 430 times higher at developed reef sites than at corresponding sites in the undeveloped areas. These differences were generally consistent with modeled sediment yields, which were 12.6 times higher for the developed compared to the undeveloped watershed. Table 1. Marine sediment major and trace element concentrations (top) and flux rates (bottom) plotted by developed sites in Coral Bay and undeveloped sites in Lameshur Bay. Acknowledgements: This work has been supported by funding from the NOAA Coral Reef Conservation Program and NOAA/ARRA to the VI-RC&D. Thanks to San Diego State University Geological Sciences Laboratory and the Washington State University Geoanalytical Laboratory for their help and training with XRF and XRD. Also thank you to Aaron Pietruszka, AmaliaDeGrood, Whitney Sears, Zoe Hastings, Thomas DeCarlo, Amanda Greenstein, Nick Przyuski, Esther Araiza, DeseraeRawling, Marverick Carey, Yi-Chen Hsieh, Matt Knoblock, Napoleon Guidino and USVI community field assistants including Phil Strenger, Hewitt Schlereth, Roy Proctor and Bruce Swanson. • References: • Brooks, G.R., Devine, B., Larson, R.A., Rood, B.P. (2007). Sedimentary development of Coral Bay, St. John, USVI: A shift from natural to anthropogenic influences. Caribbean Journal of Science 43(2): 226-243. • Gray, S.C., Sears, W.T., Kolupski, M.L., DeGrood, A.M., and Fox, M.D. (2012). Factors affecting land-based sedimentation in coastal bays, US Virgin Islands. Proceedings of the 12th International Coral Reef Symposium, Cairns, Australia July 9th-13th, 2012.  • Ramos Scharrón, C. E. (2010). "Sediment production from unpaved roads in a sub-tropical dry setting -- Southwestern Puerto Rico." Catena 82(3): 146-158. • Ramos-Scharrón, C. E. and L. H. MacDonald (2007). "Runoff and suspended sediment yields from an unpaved road segment, St John, US Virgin Islands." Hydrological Processes 21(1): 35-50. • Ramos-Scharrón, C.E., Atkinson, S., Day, K., Devine, B., Reale-Munroe, K., Swanson, B. (2012). “USVI Coastal Habitat Restoration Through Watershed Stabilization Project;” NOAA-ARRA: 2009-2012 – Terrestrial Monitoring Component Final Report. Unpublished report submitted to NOAA-CRP. • Williams, J. J., Dutton J., Chen C.Y., Fisher N.S., (2010). "Metal (As, Cd, Hg, and CH3Hg) Bioaccumulation from Water and Food by the Benthic Amphipod LeptocheirusPlumuous." Environmental Toxicology and Chemistry 29(8): 1755-1761